The focusing and confinement of charged particle beams, e.g., those comprised of electrons, protons, ions, etc, for use in various different applications is well known. Such charged particle beams are commonly utilized in cathode ray tubes, charged particle accelerators, x-ray/gamma ray generators, etc.
More particularly, traveling wave tubes (TWT's) commonly use periodic permanent magnet (PPM) focusing and confinement systems. As those skilled in the art will appreciate, the use of such periodic permanent magnet focusing and confinement systems provides optimal utilization of the magnet material and thereby minimizes both the weight and cost of the traveling wave tube.
The weight of the magnet material required in such periodic focusing devices is substantially less than that required for a straight-field magnet since the leakage fields thereof are confined to a diameter comparable to the magnet period, rather than to the entire length of the magnet, as would be the case for a straight-field magnet. As those skilled in the art will appreciate, the quantity of magnetic material required in such application is directly proportional to the volume of the space which must be filled by the resultant magnetic field.
The use of periodic focusing is well known in the art. The practice of such periodic focusing utilizes a magnetic field which is symmetrical about the beam axis and which periodically reverses in direction. Thus, the magnetic field functions as a series of convergent magnetic lenses which overcome the tendency of the electron beam to diverge under the influence of forces due to its own space-charge.
Moreover, the increasing need for light weight radars, such as those which may be utilized in automobiles, missiles, remotely piloted vehicles, etc. has increased the need for traveling wave tubes having lower weights.
Thus, according to contemporary methodology, a traveling wave tube generally comprises a plurality of magnets configured as short, hollow cylinders (washers) which are magnetized axially in alternating directions so as to form a periodic magnetic field. Typically, iron pole-piece washers are positioned between adjacent magnets so as to concentrate the flux thereof in the volume occupied by the electron beam.
Knowledge of the full magnetic field structure generated by such periodic permanent magnet focusing and confinement systems is frequently required so as to facilitate accurate modeling of the electron beam propagation therein and also so as to facilitate optimization of the focusing and confinement system. Thus, proper modeling and optimization of the magnetic field is essential to the successful design of high performance vacuum electronic devices employing periodic permanent magnetic focusing and confinement.
Although it is possible to attempt optimization of the magnetic field for use in periodic permanent magnet focusing and confinement systems via trial and error, such an iterative process is extremely time consuming and does not guarantee the desired level of optimization. Such a trial and error approach to magnetic field optimization involves making subtle changes to the magnetization level of one or more of the magnets of a periodic permanent magnetic system and then using an electromagnetic solver such as MAXWELL, by Ansoft Corporation of Pittsburgh, Pa.
However, as those skilled in the art will appreciate, such an iterative approach may be extremely time consuming because of the non-intuitive magnetization required to provide the desired resultant magnetic field. As such, it is desirable to provide a means for calculating the required magnetization of each magnet of a periodic permanent magnetic system so as to provide the desired resultant total magnetic field.